The present invention relates to a method and an apparatus for determining a rotational angular center of a rotary body, and more particularly to a method and an apparatus for determining a rotational angular center of a rotary body rotating in cooperation with a steering wheel of an automobile and the like.
Hitherto, in vehicles including automotive vehicles a rotary disk which rotates in cooperation with the steering wheel is provided. A plurality of slits are provided an equiangular distance in the rotary disk, and two photo-interrupters are disposed closely to the rotary disk to face the slits. A light passing through the slit is detected by the photo-interrupters, thereby information relating to the steering is obtained and used to conduct various controls. Namely, the two photo-interrupters produce pulse like electric signals which are the same in the waveform but nearly 90 degrees out of phase from each other. The electric signals are counted to detect a rotational direction and a rotational angle of the steering wheel.
However, there is no means to correct an error in such a conventional rotational angular detector, in such a case that an erroneous count occurs in the counter due to electric noises etc., resulting in the problem that the system erroneously operates according as the errors are accumulated. Moreover, when there is employed a power cut off method in which the power feed to the rotation angular detector is cut off after the power supply is switched off in order to lessen power consumption, a change of an angular position of the steering wheel until the ignition switch is turned on next time results in an error and such errors are accumulated.
In addition, since the rotational angle detector produces same output value per each 360 degrees rotation of the steering wheel in clockwise and counterclockwise directions, it is impossible to discriminate between the steering angular position when the vehicle advances in a beeline and a steering angular position after the steering wheel has made one revolution, resulting in the possibility that the various controls are erroneously conducted.